This invention relates generally to local area networks (LANs) of computers and, more particularly, to multiple LANs that are interconnected by bridges and routers. More specifically, the invention is concerned with a problem that arises in interconnected networks using a set of protocols generally known as TCP/IP. TCP stands for Transmission Control Protocol, and IP is Internet Protocol. The following background material introduces various computer network concepts and definitions. Those familiar with computer networks and TCP/IP may wish to skip to the subsection headed "The Problem."